Holey Fiber, also called Crystal Fiber, was first developed at the University of Bath in 1995 based on the work of Philip Russell. Unlike normal optical fiber which is solid throughout, holey fiber is fabricated with one or more continuous open channels running from one end to the other. These can be very small diameter channels, with diameters of 3 micrometers and less being possible today. Holey fiber may be made from glass or plastic. These channels have previously been filled with gas in an application to develop a high-power laser. Recently, holey fiber has been investigated for use in medical applications within the endoscope subject area, in which viewing of the interior of the body is the purpose. This work was done by Martijn van Eijkelenborg, Australian Photonics Cooperative Research Center, University of Sydney, Australia. A short paper on this topic is M. A. van Eijkelenborg, “Imaging with microstructured polymer fibre,” Opt. Express 12, 342-346 (2004).
In this case the holey fiber is used for passing optical frequencies, there are optical frequencies traveling in both directions, and the application is viewing of the interior of the cavity. It is interesting to consider, however, whether holey fiber can be used for other medical purposes, such as a combined device in which both electromagnetic energy and physical objects are passed along the channels. This field of study would usually be called capillary optics or capillary devices, however a key difference between holey fiber (also sometimes called crystal fiber or photonic band-gap fiber) and capillary tubes is that the electromagnetic confinement ability of the holey fiber is much better than a capillary tube.
Holey fiber can be manufactured to (1) provide what are effectively multiple capillary tubes capable of passing liquids, gels, gasses and solid objects, while also (2) preserving the ability to carry and confine electromagnetic radiation either in optical, infrared, microwave or RF form, from one end to the other. The unique property of light guidance was recognized by Benabid, Knight and Russell [“Particle levitation and guidance in hollow-core photonic crystal fiber”, F Benabid, J C Knight, P. St. J Russell, Optics Express 21 Oct. 2002 vol 10(21) 1195] as a key difference between holey, crystal, photonic bandgap fibers and their related capillary tubing cousins. Also, just as optical fiber can carry light, it can also carry microwaves or other electromagnetic radiation. It is also possible for different channels within the same holey fiber to be manufactured to guide different wavelengths.
How can these unique holey fiber properties be used to improve breast imaging for the purposes of breast disease analysis, breast cancer detection and treatment, and improvements in breast surgery? As well, what are the implications of this unique fiber family in the design of micro-catheters for other medical operations, such as intravascular inspection and treatment?
Breast imaging for the purposes of finding cancerous lesions is an important industry and technology area because breast cancer is a leading cause of death for female adults. Many methods have been tried in the industry, as reviewed in the book “Mammography and Beyond”, as discussed at workshops such as Workshop on Alternatives to Mammography 2004 in Winnipeg, and as discussed within the relevant research literature such as TCRT (Technology in Cancer Research and Treatment), IEEE Medical Imaging, and other publications.
The methods that have been discussed include X-Ray imaging (film and full-field digital mammography), thermography (in which hotter local areas are indicative of increased blood flow, potentially indicating tumor growth), ultrasound imaging, MRI (Magnetic Resonance Imaging), optical and infrared imaging at various frequencies using various techniques, microwave and RF imaging at various frequencies using various techniques, PET imaging (in which injections occur to cause positron radiation), contrast enhanced imaging (in which breast ducts are insufflated with appropriate fluids or gases to allow increased contrast), SPECT imaging (in which photon emissions occurs, instead of positrons as in PET, but injections are again required), fluorescence techniques, etc. For most of these methods, the basic configuration is the same, in that the imaging reception and transmission equipment is external to the breast. Relatively new techniques, such as Optical coherence tomography and Photon Migration Spectroscopy, have been developed for imaging with ultrahigh resolution. Additional and newer detection methods use genetic markers for breast cancer. There has also been work on the visual inspection of the interior of the breast duct using ductoscopes, and work on the obtaining of nipple aspirate fluid and its evaluation. Additional interesting research work has occurred in the area of Bio-Mems designs (“A Bio-Mems Device for Separation of Breast Cancer Cells from Peripheral Whole Blood”, Juan Feng, M.S.M.E. Thesis, Dept. of Mechanical Engineering, Louisiana State University, 2003-12-18).
In 2001, a report discussed the state of the art in catheter-based imaging. These authors indicated that Optical Coherence Tomography (OCT) was investigated, and that a catheter designed with an OCT capability was able to image approximately 0.5 mm around a porcine vein. Similarly, the inventor of the OCT technique (Fujimoto from MIT) discussed OCT imaging inside the body using a catheter based technique in 1999. These reports did not mention the use of in-duct detectors or transmitters being used with outside-the-breast transmitters or detectors.
Many patents have been filed in relation to breast imaging and breast cancer. In 1974, a method was outlined for aiding in the detection of breast cancer (U.S. Pat. No. 3,786,801) with the method being for the use of nipple aspirate fluid and methods to extract the fluid. In 1985, U.S. Pat. No. 4,556,057 discussed the use of an excimer laser, a light pipe, and the fluorescence of the cancer in detecting cancerous areas. The method of luminescence was used in U.S. Pat. No. 4,930,516, granted Jun. 5, 1990, entitled Method for detecting cancerous tissue using visible native luminescence.
U.S. Pat. No. 5,813,988 entitled “Time-resolved diffusion tomographic imaging in highly scattering turbid media”, claims a method of measuring and converting a diffused optical signal through the breast into an image of the breast, such that breast cancer or other problems can be detected. In this case the authors are using a trans-illumination approach to the breast imaging problem, which is different than introducing an imaging receiver or transmitter into the breast itself.
Microwave methods related to breast cancer are discussed in U.S. Pat. Nos. 6,768,925; 6,421,550; 5,983,124; 5,779,635; 5,662,110. These patents discuss the use of microwave detection of tumours within the breast, discrimination methods between malignant and benign breast tumours, and treatment of breast cancer.
Optical methods for breast cancer detection, including detection of lesions and discrimination of cancerous and non-cancerous lesions via various techniques, have been discussed in U.S. Pat. No. 5,876,339.
Implantable illuminators for therapy of the breast have been outlined in U.S. Pat. No. 6,027,524. This patent mainly discusses the design of a “cup” for imaging uniformly near the nipple area, and then discusses the post-surgery implantation of a device. This patent discusses the treatment of post-surgical tissue using photodynamic therapy, with the photodynamic therapy delivered using a rigid or almost rigid “cup” around the breast. However, there is no teaching of inserting a ductascope into the nipple while the cup is in place.
U.S. Pat. No. 6,846,311 from Acueity, granted Jan. 25, 2005 and entitled “Method and apparatus for in VIVO treatment of mammary ducts by light induced fluorescence” claims a micro-catheter which will excite a given area, receive the fluorescence of the area, thereby determining whether cancerous cells are located there or not, and will then necrose the cancerous area through the delivery of a light source. In this case a ductal compound is introduced into the breast, the compound may be allowed to “sit” for 1 to 4 hours, and then the fluorescence method of breast cancer detection is used within the breast. This approach is completely different from the approach which is presented here, in which the receivers and transmitters are inside and outside the breast. There is also no concept of multiple receivers and transmitters inside and outside the breast.
U.S. Pat. No. 6,825,928 called Depth-resolved fluorescence instrument was invented by Liu, Ramanujam and Zhu with the patent granted Nov. 30, 2004. In this invention, they provide for a device to measure the fluorescence of a sample at various depths. The purpose of measuring this fluorescence was to detect changes in cells which indicated that cancerous growth might be starting. Within this patent they cited U.S. Pat. No. 6,014,204 entitled Multiple diameter fiber optic device and process of using the same.
Many other patents have been filed. None of those of which we are aware discuss the use of receivers and transmitters introduced into the breast duct for the purposes of receiving and/or transmitting to system elements outside of the breast. As well, none of the previous work discusses the unique abilities of holey fiber as applied to micro-catheter design.
In a review of mammary ductoscopy, which was accepted on 8 Oct. 2004 (Mammary Ductoscopy: current status and future prospects”, K. Mokbel, P F Escobar and T Matsunaga, 8 Oct. 2004, The Journal of Cancer Surgery) there was no mention of imaging from inside to outside the breast or vice-versa and no mention of placing detectors or sources inside the breast for such a purpose. There was also no mention of the benefits of holey fiber for the design of the ductoscopes and endoscopes necessary to do this function. This paper reviewed the work of Dr. James Going, indicating that:                There are three types of duct systems in the female breast, with type A being large ducts that drain the majority of the breast, type B being ducts that tapered to a minute lumen within 1 mm from the skin surface, and type C which were a minor duct population. (Other studies have found that duct sizes are typically 1-2 mm but often change during breast feeding and due to hormones).        That the implication is that only type A ducts can be investigated by Mammary Ductoscopy        That it is not known whether cancer occurs in all three types of ducts, or whether type A contains the majority of the cancer.        
This paper also noted that nipple manipulation was required to access some of the ducts, and that the majority of the ducts were not so convoluted that ductoscopy would not work. This paper noted that it is believed that 85% of breast cancer occurs directly from the epithelial lining of the mammary ducts or lobules. This indicates that 15% of the non-duct based cancers must still be detected by methods which do not inspect the duct linings, and therefore it is necessary to have some method of imaging from inside to outside and outside to inside. As well, if not all ducts are available to mammary ductoscopy, it implies that some inspection of smaller ducts should occur from adjacent ductal passages that can be accessed.
On Sep. 1, 2004 (“Endoscopically Compatible Near-infrared Photon Migration Probe, C. Lubawy and N. Ramanujam, Optics Letters Vol 29(17) pp 2022-2024) there is a description of an endoscopically compatible near-infrared photon migration probe. In this case, the authors indicate that the probe can be used endoscopically or via biopsy needle, that it is 2.3 mm in diameter (which is too large for breast duct work), that it is specifically targeted at breast cancer work based on needle biopsy, and that it is designed to be used with the PMS (photon migration spectroscopy) technique. In this paper, the authors illustrate the potential to use a receiver and transmitter which is on the same platform or fiber. This paper does not discuss imaging from the inside to the outside, or imaging from the outside to the inside.
Within the field of in-duct breast imaging, it seems therefore that there are three general classifications of imaging systems, based on whether the imaging technology looks at the duct lining (Type 1), the duct locale (Type 2, approximately the area 0 to 10 mm around the duct using reflection of the illumination off of the surrounding tissue) or the whole breast (Type 3, which occurs when the entire breast from point of detector/transmission inside the breast to point of detector/transmission outside the breast is included, using transmission through the intervening tissue). For each of these general classifications, one can use optical, infrared, microwave, thermal, ultrasound, or other imaging technologies to obtain information.
Some of the Type 1 systems have been discussed in the literature. These are visual inspection of the breast duct lining, and is normally done via endoscopy using commonly available equipment. Pictures of breast ducts are available on the Acueity website. As well, some of the patents cited above have included optical and other imaging techniques as part of their endoscopic procedure.
The work by Fujimoto on catheters that provide OCT imaging, as well as the work of the Advance Imaging Catheter team of Lawrence Livermore, provide Type 1 and Type 2 imaging depending on the imaging depth that they can achieve. The other imaging catheters within the literature that use ultrasound also use Type 2 imaging, because they do not view from inside to outside the body. Type 2 imaging is also discussed within U.S. Pat. No. 6,825,928.
To the present time, we know of no study on in-breast-duct imaging that discusses Type 3 imaging.
Described herein are systems and ductoscope equipment necessary to allow receivers and transmitters to be placed within the breast, to communicate and signal to systems and detectors and transmitters outside of the breast, and thereby to generate an improved breast imaging system.